In an environment where robots and humans coexist, safety measures of the robots for the environment are important. As such safety measures, a compliance function for buffering a collision is necessary for when a robot suddenly collides into a human or an object in an environment while performing a desired operation. As the compliance function, an elastic element such as a spring for mitigating the impact of a collision is typically attached to a robot arm which is a movable part of a robot, for example. However, in the case of using the spring to mitigate an impact, the elasticity of the spring has to be adjusted during operation of the robot, for example, by increasing the cushioning property by weakening the spring at the time of collision, and this may become one factor which makes position control of the robot arm difficult. Moreover, the elastic element such as the spring makes acceleration operation of the robot less speedy, and also, may become a factor for causing vibration at the time of operation of the robot.
Patent Literature 1 discloses a robot including a collision torque buffer mechanism for relieving a force acting on an object or the like when a robot hand collides into another object or the like with an external force of given magnitude or more. With the collision torque buffer mechanism, a connection portion between a robot hand side and a robot arm side is filled with a lubricating agent, and a coupled state between the robot hand side and the robot arm side is maintained due to the viscosity of the lubricating agent even when an external force of certain magnitude is applied to the robot arm side, but when an external force exceeding the external force of certain magnitude is applied, relative rotation between the robot hand side and the robot arm side is allowed to buffer the force that acts on an object at the time of collision.